British ferns (Filicopsida)
Sporophyte. The rhizomes creeping to erect (or decumbent); bearing scales (narrow, subulate, dark brown scales). Plants with no clear distinction into fertile and sterile leaves.
Leaves aggregated terminally; to 5–20 cm long (? - plants smaller than those of A. obovatum); persistent; circinnate; compound; complexly divided; once pinnate, with conspicuously divided pinnae. Pinnae 8–20 on each side of the leaf. The petioles shorter than the blades to about as long as the blades (from about half as long to almost as long, green like the rachis, scaly at the extreme base); vascularised via a single strand (representing fusion of a pair of leaf traces). Leaf blades in outline oblong to elliptic, or lanceolate; leathery to herbaceous. The longest pinnae around the middle of the blade to above the middle of the blade; 0.5–4 cm long (?). The venation of the lamina open.
The sporangia superficial; protected; at least initially aggregated in sori. The sori linear elongated; becoming confluent when mature, or remaining discrete at maturity (?); with a true indusium. The indusia attached on one side along a vein. The mature spores monolete; with a perispore.
Distribution and habitat. Dubiously naturalized (perhaps an occasional, short-term garden escape).
Vice-county records. Britain: Buckinghamshire.
Classification. Family Polypodiaceae (C.T.W.); Aspleniaceae (Swale and Hassler); Aspleniaceae (Stace). Order Aspleniales (Swale and Hassler).
Comments. This mainland-European species was probably an erroneous inclusion in early British lists, and the present description needs critical checking. Clapham, Tutin and Warburg described A. fontanum as similar to A. obovatum, but smaller and slenderer, but Sowerby's illustration depicts a plant with once-pinnate leaves.
Illustrations. • A. fontanum: Eng. Bot. 1872 (1886). • A. fontanum: Sowerby and Johnson (1859). • Asplenium fontanum and A. obovatum (inter alia).
To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2004 onwards. British ferns (Filicopsida). Version: 4th January 2012. http://delta-intkey.com’.